A fuel cell system which is small in size and capable of performing highly efficient electric power generation has been diligently developed as a power generating system of a distributed energy supply source.
An infrastructure for supplying a hydrogen gas as a fuel necessary during an electric power generating operation of the fuel cell system is not constructed as an existing infrastructure. Therefore, a hydrogen generator configured to generate a hydrogen-containing gas using a raw material, such as a city gas or a propane gas, supplied from the existing infrastructure is normally disposed together with the fuel cell system.
The hydrogen generator includes a reformer configured to use a Ru catalyst or a Ni catalyst to cause a reforming reaction between the raw material and steam at 600 to 700° C. The hydrogen-containing gas is generated by the reforming reaction of the reformer. In addition, the hydrogen generator includes a shift converter portion configured to use a Cu—Zn based catalyst or a precious metal based catalyst to cause a shift reaction between carbon monoxide of the hydrogen-containing gas and the steam at 200 to 350° C., thereby reducing the carbon monoxide. Further, the hydrogen generator includes a reaction portion, such as a selective oxidizer, configured to use the Ru catalyst or a Pt catalyst to cause a selective oxidation reaction of the carbon monoxide at 100 to 200° C., thereby further reducing the carbon monoxide in the hydrogen-containing gas.
It is known that even after the fuel cell system stops and the supply of the raw material and water to the reformer stops, volume expansion of the water in an evaporator occurs by remaining heat of the hydrogen generator, and a residual gas in the reformer is purged (see PTL 1, for example).